Acute chest syndrome (ACS) is the leading cause of death for individuals with sickle cell disease (SCD). Current treatment for ACS is transfusion, which is complicated by alloimmunization, reactions, and infection. Additional therapies for ACS are desperately needed. The objective of this application is to determine the feasibility of conducting a clinical trial examining a novel agent, regadenoson, for the treatment of ACS in individuals with SCD. We have abundant preliminary data in murine models and patients with SCD to suggest that regadenoson, an adenosine2A receptor agonist, may interrupt ischemia/reperfusion injury (IRI) by targeting invariant NKT cells and decrease the severity of ACS episodes. We are currently performing a phase I dose finding and safety study of regadenoson in children and adults with SCD. Our ultimate goal is to extend the findings of the phase I study to the treatment of ACS. We plan to perform a multi-center, randomized phase IIb trial comparing regadenoson plus standard therapy versus standard therapy alone for ACS using length of stay as the primary outcome. We have assembled a consortium of seven institutions led by experienced SCD investigators to participate in this multi-center trial. This planning grant will be used to generate the data necessary to appropriately design the phase IIb study. In this application, we will: 1) determine whether sufficient numbers of patients with ACS can be accrued in our study consortium; and 2) measure the variance in length of stay among individuals with SCD and ACS who are receiving regadenoson. We will treat 20 participants with HbSS/HbS-thalassemia0, ages 14 to 70 years, who are admitted to the hospital for mild to moderate ACS episodes. Participants will receive a 48 hour infusion of a safe and biologically effective dose of regadenoson that will be added to standard therapy elected by the patients' physicians. We estimate that the incidence of ACS episodes in our consortium is 10 per month. Conservatively, we estimate that 1 patient will be enrolled for every 10 ACS episodes and over the 24 month funding period (enrolling about 1 patient per month) we will meet our accrual goal. Based on the data generated from this study, we plan to submit an R01 to support the phase IIb clinical trial. We anticipate that regadenoson may ultimately be used as an adjunct to transfusion therapy or may obviate the need for transfusion in some cases of ACS.